The proposed work concerns an investigation of certain aspects of the regulation of genetic transcription during cell differentiation in higher organisms - with emphasis upon the structure and function of the multiple forms of DNA-dependent tRNA polymerase present in eukaryotes. The transcription of specific genes (e.g. ribosomal and 5s RNA) will be examined in Xenopus laevis during oocyte maturation, embryonic development, and the estradiol-induced synthesis of yolk proteins in adult liver. The enzymes will be purified from these various sources and compared structurally and functionally. In addition to subunit analysis, the ability of each of the enzymes to specifically transcribe purified genes will be examined. In addition, attempts will be made to define other components which affect transcription qualitatively or quantitatively and which interact either with the enzyme(s), the template(s) or with both.